1. Field of the Invention
The present invention relates to an apparatus for vulcanisation and moulding of tyres for vehicles wheels and to a method of manufacturing said apparatus.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures integrated into the regions usually identified with the name of “beads”, having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective mounting rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers disposed in radially superposed relationship relative to each other and to the carcass ply, having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band also made of an elastomeric material like other semifinished products constituting the tyre is applied to the belt structure, at a radially external position.
In addition, respective sidewalls of elastomeric material are applied at an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads, which sidewalls can also be made in advance, in the form of drawn or extruded section members.
Subsequently to building of the green tyre carried out by assembling respective components, a vulcanisation and moulding treatment is carried out which aims at determining the structural stabilisation of the tyre through cross-linking of the elastomeric compounds, as well as at impressing the tread band with a desired tread pattern.
The vulcanisation and moulding treatment is carried out by introducing the green tyre into a moulding cavity of a vulcanisation and moulding apparatus, which cavity has a conformation corresponding to the outer conformation to be given to the vulcanised tyre.
The green tyre, once enclosed in the apparatus, is pressed against the containment walls. Subsequently or simultaneously with the pressing step, heat is supplied to the tyre pressed against the containment walls.
By effect of pressing, suitable ridges provided on the apparatus sectors and plates give rise to formation of a desired tread pattern on the tread band of the tyre, as well as of a plurality of graphic signs on the tyre sidewalls. The supplied heat causes cross-linking of the elastomeric material of which the tyre itself is made. When the cycle has been completed, the vulcanised and moulded tyre is removed from the apparatus, after opening of same.
In tyres of the winter type the tread pattern is suitable for travelling on snow-covered surfaces as well. Of the greatest importance to the aims of the behavioural features in case of running on a snow-covered roadway is the presence of a suitable series of sipes in the blocks. i.e. of a thick series of narrow cuts or hollows disposed consecutively close to each other in a circumferential direction and oriented in a way substantially transverse to the rolling direction. The task of these sipes is substantially to efficiently receive and retain the snow, since it is known the snow-to-snow friction is greater than rubber-to-snow friction.
In order to obtain said sipes on the tread, following vulcanisation and moulding, the mould is provided with a plurality of lamellae projecting from its inner surface delimiting the moulding cavity. These lamellae extend away from the surface itself. Typically, in tyre manufacture said lamellae are produced separately from the mould and subsequently mounted thereon.
Generally however, after a few work cycles of the mould, the lamellae fastened in accordance with the known art have a tendency to detach themselves from the mould and get lost. In particular, on drawing of the tyre from the mould, after a vulcanisation and moulding step has been carried out, some of the lamellae fastened according to the known methods come off the mould, and remain entrapped in the elastomeric material of the tread and/or fall to the ground.
U.S. Pat. No. 6,827,566B1 shows a self-locking lamella used in moulds for tyres. An end portion of the lamella is inserted into a slit in the mould and a main portion of same extends from the slit so as to form a narrow cut in the tyre. A wing, or a pair of wings, attached to said end portion is received in a hollow in the slit and a wedge belonging to the wing itself is able to force the wing to a locked condition while the lamella is being fitted into the slit. A thin frangible portion or a pair of frangible portions keep the wedge attached to the wind and break to enable movement of the wedge and obtain locking when the lamella is being fitted in the slit. Alternatively, the wedge is previously positioned in a housing in the hollow and the wing portions move to the locked condition when they come into contact with said wedge.
Document EP1719598A1 shows a method of fastening a lamella to a mould for tyres. A groove is formed in the mould. In a transverse section, the groove has a straight guide portion facing up on the inner surface of the mould as well as a portion of greater width formed more deeply and connected to the guide portion by a step. The lamella at one end designed to be inserted into the groove has a bent portion that when the lamella is pushed into the portion of greater width, is snap engaged with the step.
Patent JP60097811 discloses a mould for tyres comprising a ring mounted within a support body of the mould, which ring has a shape matching that of the tyre to be vulcanised and moulded, and a plurality of lamellae. The ring is provided with through openings having different shapes and the lamellae are each inserted and welded in a respective through opening. The ring is installed on the support body through bolts.